Method of electrodeposition coating on a hub

ABSTRACT

A method is realized for easily performing, without using a masking tape, an operation to accurately form a coating film  31  only on a coated section (α 8 ) partly formed on the surface of a hub main body  13   a.    
     The upper end face of a rubber closed end cylindrical masking cover  32  is elastically pressed against the outside end surface of a cylindrical section  16  forming the hub main body  13   a . As a result a border section between the coated section (α 8 ) and the portion adjacent to the coated section (α 8 ) can be made liquid-tight. In this state, coating particles are electrodeposited on the coated section (α 8 ) by bringing a coating liquid  28  discharged from a liquid supply tube  29  into contact with the coated section (α 8 ). By adopting such a method, the problems can be solved.

TECHNICAL FIELD

A method of electrodeposition coating on a hub according to the present invention is used for forming an antirust coating film on a surface of a cylindrical section provided on an outside end section of a hub that constitutes a wheel support hub unit.

BACKGROUND ART

A wheel 1 that constitutes a vehicle wheel and a rotor 2 that constitutes a disk brake, which is a braking rotating member serving as a braking device, are rotatably supported on a knuckle 3 that constitutes a suspension device, by a structure shown in FIG. 25 for example. That is, an outer ring 6 that constitutes a wheel support hub unit 5 is fixed by a plurality of bolts 7 to a circular shaped support hole 4 formed in this knuckle 3. Meanwhile, the wheel 1 and the rotor 2 are joined and fixed by a plurality of studs 9 and nuts 10 onto a hub 8 that constitutes this wheel support hub unit 5.

A double-row of outer ring raceways 11 a and 11 b are formed on an inner peripheral surface of the outer ring 6, and a joint flange 12 is formed on an outer peripheral surface. Such an outer ring 6 is fixed on the knuckle 3 by fixing the joint flange 12 by the respective bolts 7 onto the knuckle 3.

Meanwhile, the hub 8 is constructed with a hub main body 13 and an inner ring 14. An attachment flange 15 is formed on a part projecting from an outside end opening of the outer ring 6 on one part of the outer peripheral surface of the hub main body 13. (“Outside” in an axial direction refers to downside in each diagram except for FIG. 5, FIG. 25 and FIG. 26 and left side in FIG. 25 and FIG. 26, which is the outside in a width direction of a vehicle when assembled in an automobile. On the other hand, “inside” in the axial direction refers to the upper side in each diagram except for FIG. 5, FIG. 25 and FIG. 26 and right side in FIG. 25 and FIG. 26, which is the center side in the width direction of the vehicle when assembled in an automobile. This applies to the entire present specification and the entire claims.) Moreover, a cylindrical section 16 called a pilot section is provided on the outer end section of the hub main body 13 so as to be concentric with the hub main body 13. The wheel 1 and the rotor 2, having been positioned in a radial direction by being fitted onto this cylindrical section 16, are joined and fixed by the respective studs 9 and nuts 10 onto an outside surface of the attachment flange 15.

Moreover, an inner ring raceway 17 a opposing to the outer ring raceway 11 a on the outside of the double-row of outer ring raceways 11 a and 11 b is formed on the middle section of the outer peripheral surface of the hub main body 13, and a small diameter step section 18 is formed on the inner end section of the same. The inner ring 14 is fitted onto this small diameter step section 18. An inner ring raceway 17 b opposing to the outer ring raceway 11 b on the inside of the double-row of the outer ring raceways 11 a and 11 b is formed on the outer peripheral surface of this inner ring 14. Such an inner ring 14 is fixed onto this hub main body 13 by a crimped section 19 formed by plastically deforming the inside end section of the hub main body 13 outward in the radial direction. A plurality of rolling bodies 20 are respectively rollably provided between the respective outer ring raceways 11 a, 11 b and the respective inner ring raceways 17 a, 17 b. In the example shown in the diagram, the inner ring raceway 17 a on the outside is directly formed on the middle section of the outer peripheral surface of the hub main body 13, however, this inner ring raceway 17 a on the outside may be formed on the outer peripheral surface of a separate inner ring 14 a that is fitted onto the middle section of the hub main body 13 as shown in FIG. 25 with a double-dashed chain line (imaginary line). Moreover, in the example shown in the diagram, a ball is used as each of the rolling bodies 20, however, a tapered roller may be used in the case of a hub unit for a heavy automobile. Furthermore, opening sections of both ends of a cylindrical shaped space in which the respective rolling bodies 20 have been installed are respectively sealed by seal rings 21 a and 21 b.

Furthermore, in the example shown in the diagram, since it is a wheel support hub unit 5 for a driving wheel (front wheels of FF vehicle, rear wheels of FR/RR vehicle, or all wheels of 4WD vehicle), a spline hole 22 is formed in a center section of the hub 8. A spline shaft 24 fixed on an outside end surface of a constant velocity joint outer ring 23 is inserted in this spline hole 22. Along with this, by screwing a nut 25 onto a tip end section of this spline shaft 24 and further tightening it, the hub main body 13 is tightly held between this nut 25 and the constant velocity joint outer ring 23.

Next, FIG. 26 shows a second example of a conventionally known wheel support hub unit for a driven wheel (rear wheels of a FF vehicle and front wheels of a FR/RR vehicle). Since a wheel support hub unit 5 a of this second example is for a driven wheel, the spline hole is not provided in the center section of the hub main body 13 a that constitutes a hub 8 a. Also in the case of the present example, the inner ring raceway 17 a on the outside is directly formed in the middle section of the outer peripheral surface of the hub main body 13 a, however, the inner ring raceway 17 a on the outside may be formed on an outer peripheral surface of a separate inner ring (not shown in the diagram) that is fitted onto the middle section of the hub main body 13 a. Moreover, in the example shown in the diagram, the inside end surface of the inner ring 14 is held by the crimped section 19 provided on the inside end section of the hub main body 13 a, however, the inside end surface of the inner ring 14 may be held by a nut screwed onto the inside end surface of the hub main body 13 a. In this case, a male screw section is provided on the inside end section of the hub main body 13 a for screwing the nut. Other constructions and effects of the other parts are similar to those of the first example described above.

Incidentally, in the case of the wheel support hub units 5 and 5 a described above, a coating film is formed to protect against rust and so forth on at least one part of the surface of the cylindrical section 16 in the hub main bodies 13 and 13 a. A specific range (“desired range”) of a surface to be coated on which such a coating film is to be formed differs as shown with the broken lines α₁ to α₈ in (A) to (H) in FIG. 27 for example, depending on the purpose of the coating film. Moreover, as a method of forming a coating film on the surface to be coated, various methods such as a brush coating method or an electrodeposition coating method are conventionally known (for example, refer to Patent Documents 1 and 2, specifically, Japanese Patent Application Publication No. 2003-136902 and Japanese Patent Application Publication No. 2003-342793). Among these methods, compared to use of other methods, the use of the electrodeposition coating method is more preferable not only because it is able to evenly form a thin coating film on the surface to be coated, but also because it is able to shorten a length of time required for drying when baking this coating film on the surface to be coated, and is able to realize a coating film that is unlikely to peel off from the surface to be coated.

FIG. 28 shows an example of the electrodeposition coating method disclosed in Patent Document 2. In the case of the present example, the surface to be coated is a part shown with the broken line α₁ in FIG. 28 and FIG. 27 (A), that is, an outer peripheral surface of an outside half part, an inner peripheral surface of the outside half part, and an outside end surface, of the cylindrical section 16 that constitutes the hub main body 13. When forming a coating film on such a surface to be coated (α₁), first, preprocessing such as degreasing cleaning is carried out on this surface to be coated (α₁). Next, as shown in FIG. 28, with an electrode 30 a fixed on a top surface of a supporting base 26 brought into contact with the hub main body 13 and an outside surface of the attachment flange 15 that constitutes this hub main body 13 supported on a supporting base not shown in the diagram, the outside half part of the cylindrical section 16 is dipped in a coating liquid 28 filled in a coating liquid tank 27. Thus, this coating liquid 28 is brought into contact with the entire surface to be coated (α₁). The operation of dipping at this time is carried out by continuously supplying the coating liquid 28 into the coating liquid tank 27 through a liquid supply pipe 29 while overflowing this coating liquid 28 from a top end edge of this coating liquid tank 27. The reason for carrying out the dipping operation in this way is to maintain the position of the liquid surface of the coating liquid 28 and to appropriately regulate a coating range of the cylindrical section 16.

Once the coating liquid 28 has come into contact with the entire surface to be coated (α₁) as described above, subsequently, in this state, a voltage is applied between an electrode 30 b installed in the coating liquid 28 and the electrode 30 a in contact with the hub main body 13 (for example, respectively, the electrode side 30 b is connected to a positive pole and the electrode 30 a side is connected to a negative pole). As a result, an undried coating film 31 is formed on the surface to be coated (α₁) by ionizing the coating particles in the coating liquid 28 and electrodepositing these ionized coating particles on the surface to be coated (α₁). Next, the cylindrical section 16 is taken out from the coating liquid 28, this undried coating film 31 is heated to dry it, and thereby this coating film 31 is baked onto the surface to be coated (α₁). Lastly, this coating film 31 is cooled and coating operation is complete. In the example shown in the diagram, this coating film 31 is shown with a heavy line for the sake of simplicity, however, the width of this heavy line does not represent the thickness of this coating film 31. The actual thickness of the coating film 31 is, for example, approximately several μm once it has been subjected to baking, depending on the length of time for which the above mentioned electric voltage has been applied. This point is the same as that in another conventional method described later and as that in the embodiments of the present invention.

As described above, in the case of the conventional electrodeposition coating method shown in FIG. 28, as a method of bringing the surface to be coated into contact with the coating liquid 28, a method of simply dipping a part of the hub main body 13 in the coating liquid 28 filled in the coating liquid tank 27 is employed. In such a conventional electrodeposition coating method, in the case where the entire surface of the dipped part becomes a surface to be coated when a part of the hub main body 13 is dipped in the coating liquid 28 (for example, in the case of forming the coating film 31 on this surface to be coated up to a same position in the axial direction on both the inner and outer peripheral surfaces of the cylindrical section 16 as shown in FIG. 27 (A) and FIG. 28 with broken line α₁), there will be no particular problem. However, in the case where only one part of the surface of the dipped part becomes the surface to be coated (for example, when the positions of the end sections of the coating film 31 of this surface to be coated on both the inner and outer peripheral surfaces of the cylindrical section 16 differ from each other in an axial direction as shown in FIG. 27 (B) to (H) with broken lines α₂ to α₈), the coating range cannot be appropriately regulated as parts other than this surface to be coated also come into contact with the coating liquid 28. In this case, only the surface to be coated can be brought into contact with the coating liquid 28 if dipping is carried out with a masking tape attached to the parts other than the surface to be coated, however, since there is a need for carrying out operations of attaching and removing the masking tape before and after the dipping operation, the coating operation becomes troublesome.

Furthermore, in the case where the coating film is formed by means of electrodeposition coating on the outside end portion to middle portion of the outer peripheral surface, the outside end surface, and the inner peripheral surface of the cylindrical section 16 and on the part of the outside end surface of the hub main body 13, the circumference of which is surrounded by the cylindrical section 16 (the part shown with the broken line α₆), first, preprocessing such as degreasing cleaning is carried out on the part shown with the broken line α₆.

Next, the operation of electrodepositing coating particles on the part shown with the broken line α₆ (the operation of forming an undried coating film 54) is carried out using a coating device 46 such as is shown in FIG. 30 for example. The coating device 46 is provided with: a coating liquid tank 48 that is filled with a coating liquid 47 and has an opening on the top end thereof; a recovery tank 49 that is provided around this coating liquid tank 48 to collect the coating liquid 47 that is overflowed from the top end edge of this coating liquid tank 48; and a nozzle 52 that is provided in a vertical direction passing through center sections of respective bottom plate sections 50 and 51 that constitute these coating liquid tank 48 and the recovery tank 49 so as to be air-tight and liquid-tight, and that injects the coating liquid 47 from the top end opening thereof by action of a pump not shown in the diagram. On the top end section of this nozzle 52, a guide section 53 is provided with a shape in which this entire top end section has been bent back outward in the radial direction into a U-shape. Moreover, the top end edge of this nozzle 52 is arranged above the surface of the coating liquid 47 filled in the coating liquid tank 48.

In the case where the coating particles are electrodeposited on the part shown with die broken line α₆ using such a coating device 46, as shown in the diagram, the outside end portion to middle portion of the cylindrical section 16 is dipped in the coating liquid 47 filled in the coating liquid tank 48. Meanwhile, an outer surface of the guide section 53 provided on the top end section of the nozzle 52 is made to oppose across its entirety the part of the outside end surface of the hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16, and the inner peripheral surface of this cylindrical section 16. In this state, by ejecting coating liquid 47 upwards from the top end opening of the nozzle 52, this ejected coating liquid 47 is made to flow through a gap part between the above-mentioned surfaces opposing to each other, in a state where this gap part is entirely filled with the coating liquid 47. Thus, His coating liquid 47 is brought into contact respectively with the entire part of the outside end surface of the hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16, and with the entire inner peripheral surface of the cylindrical section 16. Thus, the entire part shown with the broken line α₆ is brought into contact with the coating liquid 47.

Moreover, the coating liquid 47 ejected from the top end opening of the nozzle 52 as described above is poured into the interior of the coating liquid tank 48. Then the coating liquid 47 filled in the coating liquid tank 48 overflows by the amount that has been poured in this way to the exterior from the top end edge of the coating liquid tank 48. The coating liquid 47 overflowed like this is recovered by the recovery tank 49, and it is re-used as the coating liquid 47 to be ejected from the top end opening of the nozzle 52.

Once the entire part shown with the broken line α₆ has been brought into contact with the coating liquid 47 as described above, subsequently, in this state, an electric voltage is applied between an electrode, not shown in the diagram, in contact with another part of this coating liquid 47 and the hub main body 13 a (for example, the electrode side is connected to a positive pole and the hub main body side is connected to a negative pole). As a result, by ionizing the coating particles in the coating liquid 47 and electrodepositing these ionized coating particles on the part shown with the broken line α₆, an undried coating film 54 is formed on this part. Once the undried coating film 54 has been formed as described above, thereafter, this coating film 54 is baked onto the abovementioned surface by heating this undried coating film 54 to dry it, and then this coating film 54 is cooled down to complete the coating operation.

In the case where the operation of electrodepositing the coating particles on the part shown with the broken line α₆ is carried out as described above within one step, undulations occur on the part of the surface of the coating liquid 47 filled in this coating liquid tank 48 in the radial direction outer side of the cylindrical section 16, depending on a liquid flow of the coating liquid 47 when it is ejected from the top end opening of the nozzle 52 and poured into the coating liquid tank 48. As a result, a range of the coating liquid 47 that comes in contact with the outer peripheral surface of the cylindrical section 16 changes in response to the movement of the above undulations, the shape of the edge of the coating film 54 to be formed on the outer peripheral surface of this cylindrical section 16 does not become a straight line when seen from the radial direction outer side of the cylindrical section 16 and becomes corrugated, and the coating film 54 may not be accurately formed on a part on which the coating film 54 is to be formed.

Moreover, in the case of forming a coating film on the surface of the cylindrical section 16 that constitutes the hub main bodies 13 and 13 a by means of electrodeposition coating, an electric voltage is applied between an electrode in contact with another part of this coating liquid and another electrode in contact with the hub main bodies 13 and 13 a while the surface of the cylindrical section 16 is in contact with the coating liquid. Thus, an undried coating film is formed on the surface of the cylindrical section 16 by ionizing the coating particles in the coating liquid and electrodepositing these ionized coating particles onto this surface. Subsequently, this undried coating film is heated to dry it, thereby baking this coating film onto the above surface, and then this coating film is cooled to complete the coating operation.

Incidentally, when baking the coating film onto the surface of the cylindrical section 16 as described above, inappropriate heating of the undried coating film gives rise to the following problems. Specifically, a hardened layer is formed on at least one part of the middle section to the section close to the inside end of the outer peripheral surface of the hub main bodies 13 and 13 a (for example, parts such as a base part of the attachment flange 15, a part on which the inner ring raceway 17 a has been formed, and a part with which the inner rings 14 and 14 a are engaged) by applying a high frequency hardening processing to the entire circumference of this part to improve hardness of the part. Therefore, in the case where the temperature of the hardened layer rises excessively as a result of inappropriate heating of the undried coating film, a softening effect occurs in this hardened layer (such as annealing or tempering) resulting in a problem of reduction in the hardness of this hardened layer. Furthermore, in the case of heating the undried coating film in a state where the wheel support hub units 5 and 5 a have been assembled, if the temperature of the grease enclosed in an installation section for the respective rolling bodies 20 rises excessively as a result of inappropriate heating of this undried coating film, a problem of this grease degrading occurs.

Patent Document 1: Japanese Patent Application Publication No. 2003-136902

Patent Document 2: Japanese Patent Application Publication No. 2003-342793

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In consideration of the above described problems, a method of electrodeposition coating on a hub according to a first aspect of the present invention has been invented to realize an easy operation of forming a coating film only in a desired range on a surface of a hub without using masking tape.

Moreover, in consideration of the above described problems, a method of electrodeposition coating on a hub according to a second aspect of the present invention has been invented to realize a method that enables accurate formation of a coating film in a desired range including at least a surface of a cylindrical section among the surfaces of the hub.

Moreover, in consideration of the above described problems, a method of electrodeposition coating on a hub according to third and fourth aspects of the present invention has been invented to realize a method that can prevent an excessive increase in temperature of a part on an outer peripheral surface of the hub on which a hardened layer has been formed by means of high frequency hardening processing, or that can prevent an excessive increase in the temperature of grease enclosed in a rolling body installation section, in the case of applying heat to an undried coating film to bake the coating film onto the surface of the cylindrical section that constitutes the hub.

Means for Solving the Problem

In a method of electrodeposition coating on a hub according to a first aspect of the present invention, in order to form a coating film on a desired range that includes at least one part of a surface of a cylindrical section among the surfaces of a hub that constitutes a wheel support hub unit that is respectively provided with an attachment flange on a part close to an outside end of an outer peripheral surface for supporting and fixing a wheel and a braking rotating member, and with the cylindrical section for externally engaging at least one of the wheel and the braking rotating member on an outside end section, coating particles in a coating liquid are electrodeposited on this desired range, with the desired range in contact with the coating liquid.

In particular, in the method of electrodeposition coating on a hub according to the first aspect of the present invention, the operation of electrodepositing the coating particles on the desired range is carried out with a masking cover in contact with or closely opposing to a border part on the surface of the hub between the desired range and a range adjacent to this desired range.

An opposing clearance in the case of having the masking cover closely opposed to the border part is to be made as small as machine adjustment allows (preferably no greater than 1 mm (more preferably no greater than 0.5 mm)) so that even in the case where the coating liquid leaks from a gap created in this opposing section, a leak amount becomes minute.

Moreover, the method of electrodeposition coating on a hub according to the first aspect of the present invention may be carried out for a hub (single hub body) prior to assembly of the wheel support hub unit, and it may also be carried out for a hub in a condition where this wheel support hub unit has been assembled.

In a method of electrodeposition coating on a hub according to a second aspect of the present invention, in order to form a coating film on a desired range that includes at least a surface of a cylindrical section among the surfaces of a hub that constitutes a wheel support hub unit that is respectively provided with an attachment flange on a part close to an outside end of an outer peripheral surface for supporting and fixing a wheel and a braking rotating member, and with the cylindrical section for externally engaging at least one of the wheel and the braking rotating member on an outside end section, coating particles in a coating liquid are electrodeposited on this desired range, with the desired range in contact with the coating liquid.

In particular, in the method of electrodeposition coating on a hub according to the second aspect of the present invention, a plurality of partial ranges that respectively become a range of one part of the desired range are set, and the operation of electrodepositing the coating particles on the desired range is carried out in separate processes for each of the partial ranges.

Furthermore, in the case of setting the plurality of partial ranges, as long as all of the partial ranges together cover the above entire desired range, overlaps between the respective partial ranges do not cause a problem.

Moreover, the method of electrodeposition coating on a hub according to the second aspect of the present invention may be carried out for a single hub body prior to assembly of the wheel support hub unit, and it may be carried out for a hub in a condition where this wheel support hub unit has been assembled.

In a method of electrodeposition coating on a hub according to third and fourth aspects of the present invention, after forming an undried coating film on a surface of a cylindrical section among the surfaces of a hub that constitutes a wheel support hub unit respectively provided with an attachment flange on a part close to an outside end of an outer peripheral surface for supporting and fixing a wheel and a braking rotating member, and with the cylindrical section for externally engaging at least one of the wheel and the braking rotating member on an outside end section, by electrodeposition (ionized) coating particles onto the surface, the coating film is baked onto the surface of the cylindrical section by heating the undried coating film to dry it.

In particular, in the method of electrodeposition coating on a hub according to the third aspect of the present invention, the heating temperature of the undried coating film is below 140° C.

Moreover, in the method of electrodeposition coating on a hub according to the fourth aspect of the present invention, the heating temperature of the undried coating film is between 140° C. and 220° C., and the operation of heating the undried coating film is carried out while the hub is being cooled from an inside end side (the part of this hub on the inside end side of the cylindrical section).

Moreover, the method of electrodeposition coating on a hub according to the third and fourth aspects of the present invention may be carried out for a single hub body prior to assembly of the wheel support hub unit, and it may be carried out for a hub in a condition where this wheel support hub unit has been assembled.

EFFECT OF THE INVENTION

As described above, in the case of the method of electrodeposition coating on a hub according to the first aspect of the present invention, the operation of electrodepositing coating particles onto a desired range is carried out with a masking cover in contact with or closely opposed to a border part between the desired ranged of the surface of the hub and the range adjacent to this desired range (with these both ranges separated from each other). Therefore, during this operation, coating liquid that has been brought into contact with this desired range can be prevented from coming into contact with the range adjacent to this desired range. In particular, in the case of the present invention, the above described prevention effect can be achieved without attaching masking tape to this adjacent range, by only placing the masking cover in contact with, or in a condition closely opposing to, the border part. Therefore, according to the present invention, the operation of forming a coating film only on the desired range can be carried out easily.

As described above, in the case of the method of electrodeposition coating on a hub according to the second aspect of the present invention, since the operation of electrodepositing the coating particles on the desired range of the surface of the hub is carried out in separate processes for each of a plurality of partial ranges, coating of each of the partial ranges can be accurately carried out. Therefore, coating of the entire desired range can be accurately carried out.

Furthermore, according to the method of electrodeposition coating on a hub according to the third and fourth aspects of the present invention described above, when heating the undried coating film to bake the coating film onto the surface of the cylindrical section, the temperature of a hardened layer, which is a part on the outer peripheral surface of the hub upon which high frequency hardening processing has been carried out, does not rise excessively (the temperature does not rise to a temperature at which a softening effect such as annealing or tempering starts to occur in this hardened layer), and an excessive increase in the temperature of grease enclosed in a rolling body installation section that constitutes the wheel support hub unit (the temperature does not rise to a temperature at which this grease degrades) can be prevented.

Specifically, in the case of the wheel support hub unit shown in FIG. 25 and FIG. 26 mentioned above, the tempering temperature in the case of forming the hardened layer with furnace heating is between 150° C. and 180° C. Therefore, depending on a length of time for which the hardened layer is to be exposed to the temperature, as long as the temperature is maintained below 150° C., a softening effect such as tempering does not occur in the hardened layer within the length of time required for drying of the undried coating film. For example, even if the hardened layer has been exposed for 30 minutes at 140° C., a softening effect such as tempering does not occur in the hardened layer. Furthermore, in the case of the wheel support hub unit shown in FIG. 25 and FIG. 26 mentioned above, if the temperature of the grease enclosed in the rolling body installation section reaches dropping point (this varies depending on the type of grease, but an example would be about 260° C.), the grease degrades regardless of exposure time, however, up to approximately 120° C. the grease does not degrade regardless of exposure time, and at approximately 140° C. it does not degrade within a length of time required for drying the coating film (for example, no more than 30 minutes).

On the other hand, as described above, in the case of the method of electrodeposition coating on a hub according to the third aspect of the present invention, the heating temperature of the coating film is low and no greater than 140° C. Therefore, even in the case where the heat applied to this coating film is transmitted to the above hardened layer, the temperature of this hardened layer does not rise excessively. Moreover, even if this heat is transmitted to the grease, the temperature of this grease does not rise to the temperature at which degradation starts to occur.

Furthermore, as described above, in the case of the method of electrodeposition coating on a hub according to the fourth aspect of the present invention, the heating temperature of the undried coating film is raised comparatively high, within a range 140° C. to 220° C., however, the operation of heating the undried coating film is carried out while the hub is being cooled from the inside end side. As a result, an increase in the temperature of the hardened layer and in the grease due to the heat applied to the coating film can be suppressed. Therefore, softening in the hardened layer due to an excessive temperature increase, or degradation in the grease due to an excessive temperature increase can be prevented. Furthermore, in the case of the method of electrodeposition coating on a hub according to the fourth aspect of the present invention, since the heating temperature of the undried coating film is raise comparatively high, a length of time required for baking this coating film can be shortened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view that shows a first embodiment of the present invention in a state where a surface to be coated is brought into contact with coating liquid.

FIG. 2 is a sectional view that shows a state after the state in FIG. 1 where the coating liquid is drained from interior of a masking cover and air is blown into an outside end opening of a cylindrical section.

FIG. 3 is a sectional view showing a second embodiment of the present invention.

FIG. 4 is a sectional view showing a third embodiment of the present invention.

FIG. 5 is a top view of the masking cover seen from above in FIG. 3.

FIG. 6 is a sectional view for explaining a problem that occurs in the case where liquid drain passages such as cutouts on a top end edge portion of the masking cover are not provided.

FIG. 7 is a sectional view showing a fourth embodiment of the present invention.

FIG. 8 is a sectional view showing a fifth embodiment of the present invention.

FIG. 9 is a sectional view showing a sixth embodiment of the present invention.

FIG. 10 is a sectional view showing a seventh embodiment of the present invention.

FIG. 11 is a sectional view that shows an eighth embodiment in a state where a first process operation of electrodeposition coating is being carried out.

FIG. 12 is a sectional view that shows the same embodiment in a state where a second process operation of electrodeposition coating is being carried out.

FIG. 13 is a sectional view that shows a ninth embodiment of the present invention in a state where a first process operation of electrodeposition coating is being carried out.

FIG. 14 is a sectional view that shows the same embodiment in a state Where a second process operation of electrodeposition coating is being carried out.

FIG. 15 is a sectional view that shows a tenth embodiment of the present invention in a state where a first process operation of electrodeposition coating is being carried out.

FIG. 16 is a sectional view that shows the same embodiment in a state where a second process operation of electrodeposition coating is being carried out.

FIG. 17 is a sectional view that shows an eleventh embodiment of the present invention in a state where a first process operation of electrodeposition coating is being carried out.

FIG. 18 is a sectional view that shows the same embodiment in a state where a second process operation of electrodeposition coating is being carried out.

FIG. 19 is a sectional view of a hub main body to which electrodeposition coating is to be applied, showing a twelfth embodiment of the present invention.

FIG. 20 is a sectional view of the hub main body shown in a state where an undried coating film has been formed on a surface of the cylindrical section.

FIG. 21 is a sectional view of the hub main body that shows a process of baking this coating film on the surface of the cylindrical section by heating the undried coating film.

FIG. 22 is a sectional view of the hub main body that shows a process of cooling the coating film that has been baked on the surface of the cylindrical section.

FIG. 23 is a sectional view of the hub main body that shows a process of baking a coating film on the surface of the cylindrical section by heating this undried coating film in a thirteenth embodiment of the present invention.

FIG. 24 is a sectional view of the hub main body that shows a process of cooling the coating film that has been baked on the surface of the cylindrical section.

FIG. 25 is a sectional view that shows one example of a wheel support hub unit for a driving wheel in a state of being assembled to a knuckle.

FIG. 26 is a sectional view that shows an example of the wheel support hub unit for a driven wheel.

FIG. 27 is a diagram showing eight examples of ranges in which the coating film is to be formed.

FIG. 28 is a sectional view that shows a first example of a conventional electrodeposition coating method.

FIG. 29 is a sectional view of the hub main body that constitutes the wheel support hub unit for the driven wheel shown in FIG. 26.

FIG. 30 is a sectional view that shows a second example of a conventional electrodeposition coating method.

BEST MODE FOR CARRYING OUT THE INVENTION

A method of electrodeposition coating on a hub according to a first aspect of the present invention can be carried out where a border section, which is to come into contact with, or closely oppose, the masking cover, is a periphery part (outer periphery part or inner periphery part) of an outside end surface of a cylindrical section that constitutes the hub.

Moreover, in the case where a hole that passes through this hub in an axial direction is provided in a center section of the hub, the above-mentioned method can be carried out where a border section, which is to come into contact with, or closely oppose, the masking cover, is an annular section that surrounds an outside end opening of the above hole of the outside end surface of the hub which is surrounded by the cylindrical section.

Furthermore, when carrying out these embodiments of the present invention after coating particles in a coating liquid have been electrodeposited onto an inner surface of the cylindrical section in a state where the radial direction inner side of the cylindrical section that constitutes the hub is filled with the coating liquid, this coating liquid is drained to the exterior of this cylindrical section through the outside end opening of the cylindrical section, after which gas (such as air) may be blown into the outside end opening of this cylindrical section.

As a result, when draining the coating liquid from the cylindrical section, even in the case where a film of the coating liquid is formed on the outside end opening section of this cylindrical section, the above coating liquid film can be ruptured by the gas blown into this outside end opening before the masking cover is separated from the outside end opening section of this cylindrical section. Therefore, when separating the masking cover from the outside end opening of the cylindrical section, a problem of splashing the coating liquid around the hub due to the coating liquid film ruptures can be prevented.

Furthermore, when carrying out the invention mentioned above, a masking cover may be used, which has an entirely cylindrical shape, a section on the outer peripheral surface thereof close to a tip end that can be pressed against the entire inner periphery part of the outside end surface of the cylindrical section that constitutes the hub so as to be liquid-tight, and a liquid drain passage formed on a part of the tip end section able to enter within the cylindrical section that connects the outer peripheral surface and inner peripheral surface of the portion.

As a result, having electrodeposited the coating particles in the coating liquid on the inner peripheral surface of this cylindrical section in a state where the radial direction inner side of this cylindrical section is filled with the coating liquid, and after draining this coating liquid to the exterior of the cylindrical section through the outside end opening of the cylindrical section, the coating liquid can be prevented from pooling in a gap section between the outer peripheral surface of the tip end section of the masking cover and the inner peripheral surface of the cylindrical section. Therefore, a problem of coating liquid pooled in the gap section falling on surrounding objects and splashing when separating the hub and the masking cover in the vertical direction while keeping the cylindrical section facing downward, and thereby becoming attached to sections other than the coated section on the surface of the hub, can be prevented.

Furthermore, when carrying out the method of electrodeposition coating on a hub according to a second aspect of the present invention, as one of the respective processes, it is preferable to employ a process of electrodepositing the coating particles onto a section among the surfaces of the cylindrical section that is in contact with the coating liquid while only the cylindrical section is dipped in the coating liquid contained in a coating liquid tank having an open top section.

As a result, when electrodepositing the coating particles onto the outer peripheral surface of the cylindrical section while only the cylindrical section is being dipped in the coating liquid contained in the coating liquid tank, undulation can be prevented from occurring on the surface of the coating liquid. Therefore, a coating film can be accurately formed in desired places on the outer peripheral surface of the cylindrical section.

Moreover, when carrying out these embodiments of the present invention, for example, a plurality of coating devices at least provided with coating liquid tanks that contain the coating liquid, and having an open top end, are prepared, and one coating device is selected among the respective coating devices for each process, and the selected coating device is used to carry out the process.

Furthermore, when carrying out the above invention a method may be adopted wherein, for example, one coating device provided with a coating liquid tank that contains coating liquid and that has an open top end, and a nozzle that sprays the coating liquid upwards is prepared, and each process is performed using only this coating device.

Furthermore, when carrying out the present invention, for example, the relative positions of the liquid levels of the coating liquid contained in the coating liquid tank, and of the nozzle to the hub, and a way of spraying the coating liquid to be sprayed from this nozzle are changed for each of the steps.

EMBODIMENT 1

FIG. 1 and FIG. 2 show an embodiment 1 of the present invention. In the present embodiment, a hub main body 13 a that constitutes the wheel support hub unit 5 a shown in FIG. 26 mentioned above is an object of the embodiment. An inner peripheral surface of a cylindrical section 16 that constitutes the hub main body 13 a and a part of the outside end surface of the hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16 (the portion shown with the broken line α₈ in FIGS. 1 and 2 and FIG. 27 (H)), is the surface to be coated. In order to form a coating film 31 on this surface to be coated (α₈), first, preprocessing such as degreasing cleaning is carried out on this surface to be coated (α₈).

Next, an operation of electrodepositing the coating particles on the surface to be coated (α₈) is carried out. In the case of the present embodiment, when carrying out this operation, a closed end cylindrical masking cover 32, which is made of rubber and has a top end opening, is used. That is, when carrying out the above operation, first, as shown in FIG. 1, a top end surface of the masking cover 32 is elastically pressed against the outside end surface of the cylindrical section 16 around the entire circumference thereof. Accordingly, the border section between the outside end surface of the cylindrical section 16 and the surface to be coated (α₈) is separated so as to be liquid-tight. In this state, coating liquid 28 is continuously supplied into the space surrounded by the surface to be coated (α₈) and the inner surface of the masking cover 32 through a liquid supply pipe 29 provided to pass through a center section of a bottom section 33 of the masking cover 32 so as to be liquid tight. As a result, the air in this space is drained to the exterior through a drain hole 34 provided on a portion on one section of the bottom section 33 away from the liquid supply pipe 29, and the above space is filled with the coating liquid 28. Accordingly, this coating liquid 28 is brought into contact with the entire surface to be coated (α₈).

Moreover, the coating liquid 28 supplied from the liquid supply pipe 29 into the space is subsequently discharged to the exterior through the above drain hole 34, and it is reused as the coating liquid 28 to be supplied through the liquid supply pipe 29 into the space. As a result, in the case of the present embodiment, since the coating liquid 28 is continuously supplied into the above space, liquid flow can be generated in this space, so that even if gas bubbles were to remain inside this space, these gas bubbles could be prevented from staying in one place of the surface to be coated (α₈).

Once the coating liquid 28 has come into contact with the entire surface to be coated (α₈) as described above, subsequently, in this state, a voltage is applied between a first electrode (not shown in the diagram) installed in the coating liquid 28 and a second electrode (not shown in the diagram) in contact with the hub main body 13 a (for example, respectively, the first electrode side is connected to a positive pole and the second electrode side is connected to a negative pole). As a result, an undried coating film 31 is formed on the surface to be coated (α₈) by ionizing the coating particles in the coating liquid 28 and electrodepositing these ionized coating particles on the surface to be coated (α₈).

Once the undried coating film 31 has been formed on the surface to be coated (α₈), subsequently, supply of the coating liquid 28 from the liquid supply pipe 29 into the space is stopped and the coating liquid 28 within the space is drained to the exterior through the drain hole 34 as shown in FIG. 2. Moreover, when the coating liquid 28 within the space is drained to the exterior, the interior of this space becomes substantially a vacuum and a thin film of the coating liquid 28 is formed on the outside end opening section of the cylindrical section 16, blocking this outside end opening section. While in this state, if the outside end surface of the cylindrical section 16 is separated from the top end surface of the masking cover 32, at that moment the abovementioned thin film is rupture and drops of the coating liquid 28 are splashed into an exterior space. The occurrence of such a phenomenon is not preferable in terms of maintaining the cleanliness of the exterior space and in terms of preventing the coating liquid 28 from attaching to places other than the surface to be coated (α₈) on the surface of the hub main body 13 a.

Therefore, in the case of the present embodiment, once the coating liquid 28 has been drained to the exterior from the space as described above, next, air ejected from a tip end section of an air nozzle 35 provided passing through a portion close to the top end of the masking cover 32 is blown to the outside end opening section of the cylindrical section 16. As a result, the thin film of the coating liquid 28 formed on the outside end opening section of the cylindrical section 16 is ruptured and a pressure inside the above space is brought close to (preferably equal to) the exterior pressure. Next, the outside end surface of the cylindrical section 16 is separated from the top end surface of the masking cover 32, and by heating the undried coating film 31 to dry it, the coating film 31 is baked onto the surface to be coated (α₈). Lastly, this coating film 31 is cooled and the coating operation is complete.

As described above, in the case of the method of electrodeposition coating on a hub of the present embodiment, an operation of electrodepositing the coating particles on the surface to be coated (α₈) is carried out while the surface to be coated (α₈) is in contact with the coating liquid 28, in a state where the border section between the surface to be coated (α₈) and the area adjacent to this surface to be coated (α₈) (outside end surface of the cylindrical section 16) is separated by the masking cover 32 so as to be liquid-tight. Therefore, during this operation, the coating liquid 28 in contact with the surface to be coated (α₈) can be prevented from coming in contact with places other than this surface to be coated (α₈) on the surface of the hub main body 13 a. In particular, in the case of the present embodiment, the prevention effect described above can be achieved by only pressing the masking cover 32 against the above border section so as to be liquid tight, and without having to attach masking tape to places other than this surface to be coated (α₈). Therefore, in the case of the present embodiment, the operation of forming the coating film 31 only on the surface to be coated (α₈) can be easily carried out.

In the embodiment 1 described above, in order to have the surface to be coated (α₈) in contact with the coating liquid 28, a method in which the coating liquid 28 is supplied into the space surrounded by the surface to be coated (α₈) and the inner surface of the masking cover 32, filling the interior of this space with the coating liquid 28, is employed. However, when carrying out the present invention, instead of this method, a method in which the coating liquid 28 is continuously discharged upward with force from the top end opening of the above liquid supply pipe 29 to make this ejected coating liquid 28 continuously contact with the entire surface to be coated (α₈) may also be employed.

EMBODIMENT 2

Next, FIG. 3 shows an embodiment 2 of the present invention. In the present embodiment, a hub main body 13 that constitutes a wheel support hub unit 5 for a driving wheel shown in FIG. 25 mentioned above is an object of the embodiment. An inner peripheral surface of a cylindrical section 16 that constitutes the hub main body 13 and a radial direction outer half portion of a part of the outside end surface of the hub main body 13, the circumference of which is surrounded by the cylindrical section 16 (the part shown with the broken line α₉ in FIG. 3) is the surface to be coated. In the case of the present embodiment, the reason why a radial direction inner half portion of the part of the outside end surface of the hub main body 13 surrounded by the cylindrical section 16 is not included in the surface to be coated is because this radial direction inner half portion is a bearing surface of a nut 25 (refer to FIG. 25) and if this radial direction inner half portion is subjected to electrodeposition coating, the nut 25 is likely to become loose.

Therefore, in the case of the present embodiment, when carrying out an operation of electrodepositing the coating particles on the surface to be coated (α₉), as is the case with the embodiment 1 described above, a border section separates the outside end surface of the cylindrical section 16 and the surface to be coated (α₉) so as to be liquid-tight by elastically pressing the top end surface of the masking cover 32 against the outside end surface of the cylindrical section 16 as shown in the diagram. Meanwhile, a top end surface of a rubber made second masking cover 36 supported and fixed on the top end section of the liquid supply pipe 29 is elastically pressed against the radial direction inner half portion of a part of the outside end surface of the hub main body 13 surrounded by the cylindrical section 16. Thus, the border section between this radial direction inner half portion and the surface to be coated (α₉) is separated by the second masking cover 36 so as to be liquid-tight, and an outside end opening of a spline hole 22 provided in the center section of the hub main body 13 is blocked. Then, in this state, the coating liquid 28 is continuously supplied through the liquid supply pipe 29 and through a liquid supply passage 37 provided in the second masking cover 36 into the space surrounded by the surface to be coated (α₉) and the inner surface of the masking cover 32. As a result, the air within this space is drained through the drain hole 34 to the exterior and the interior of this space is filled with the coating liquid 28. Consequently, this coating liquid 28 is brought into contact with the entire surface to be coated (α₉).

In the case of the present embodiment, the tip end section of the air nozzle 35 for blowing air after the completion of the operation of electrodepositing the coating particles on the surface to be coated (α₉) in order to prevent the coating liquid from splashing, is arranged in an inside end section of the spline hole. When the electrodepositing operation is complete, the masking cover 32 and the second masking cover 36 are lowered while compressed air is discharged from the air nozzle 35. At this time, the coating liquid attached on a contact section of the top surface of the second masking cover 36 and the outside end surface of the hub main body 13 does not splash into the periphery thereof (particularly in the spline hole 22). Moreover, excessive coating liquid attached on the inner peripheral surface of this cylindrical section 16 is collected into the masking cover 32 by air flowing downward along the inner peripheral surface of this cylindrical section 16. Other constructions and effects are similar to those of the embodiment 1 described above.

Furthermore, in the embodiment 2 described above, the second masking cover 36 is supported and fixed on the top end section of the liquid supply pipe 29, however, when carrying out the present invention, the second masking cover 36 may also be supported and fixed on a separate supporting member. Moreover, with respect to the embodiment 2 described above, in the case of the present invention, by carrying out the electrodepositing operation while the cylindrical section 16 is dipped in coating liquid contained in a coating liquid tank instead of pressing the masking cover 32 against the outside end surface of the cylindrical section 16, the coating particles can also be electrodeposited on the outside end surface and outer peripheral surface (the part dipped in the coating liquid) of the cylindrical section 16 in addition to the part shown with the broken line α₉.

EMBODIMENT 3

Next, FIG. 4 and FIG. 5 show an embodiment 3 of the present invention. As is the case with the embodiment 1 shown in FIG. 1 and FIG. 2, in the present embodiment, a hub main body 13 b that constitutes the wheel support hub unit for a driven wheel is an object of the embodiment. However, in the case of the hub main body 13 b, which is the object of the present embodiment, a male screw section 38 for screwing into a nut used for pressing the inside end surface of an inner ring 14 (refer to FIG. 26) is provided in an inside end section of this hub main body 13 b. Also, in the case of the present embodiment, as with the embodiment 1 described above, an inner peripheral surface of a cylindrical section 16 that constitutes the hub main body 13 b and a part of the outside end surface of the hub main body 13 b, the circumference of which is surrounded by the cylindrical section 16 (the part shown with the broken line α₈ in FIG. 4 and FIG. 27 (H)), is the surface to be coated.

In the case of the present embodiment, a masking cover 32 a used when carrying out the operation of electrodepositing the coating particles on the surface to be coated (α₈) is constructed in a substantially cylindrical shape and is joined and fixed on a top end opening section of a closed-ended cylindrical container 39 manufactured from metal material. Accordingly, in the case of the present embodiment, the liquid supply pipe 29 is provided passing through the center section of a bottom section 40 of the container 39 so as to be liquid-tight. Moreover, the drain hole 34 is provided in a part on this bottom section 40 away from the liquid supply pipe 29.

Furthermore, in the case of the present embodiment, a top half section of the masking cover 32 a is a conical cylindrical section 41 inclined in a direction such that the radial dimension becomes smaller as it gets closer to the top side. An outer diameter dimension D41 of the greater diameter side end of this conical cylindrical section 41 is greater than an inner diameter dimension d16 of the above cylindrical section 16 (D41>d16), and an outer diameter dimension d41 of the smaller diameter side end of this conical cylindrical section 41 is smaller than the inner diameter dimension d16 of the cylindrical section 16 (d41<d16). Moreover, cutouts 42 that open on the smaller diameter side periphery are respectively provided in a plurality of places in a circumferential direction (six places in the example in the diagram) of a part of a smaller diameter side section of the conical cylindrical section 41 the outer diameter dimension of which is smaller than the inner diameter dimension d16 of the cylindrical section 16 (the part on the radial direction inner side of the broken chain line in FIG. 5). In the case of the present embodiment, each of these cutouts 42 respectively correspond to “oil discharging passages”.

In the case of the present embodiment, when carrying out the operation of electrodepositing the coating particles on the surface to be coated (α₈), as shown in the diagram, the smaller diameter side end section of the conical cylindrical section 41 that constitutes the masking cover 32 a is inserted into the interior of the cylindrical section 16, and the outer peripheral surface of this conical cylindrical section 41 is elastically pressed against the border section between the outside end surface of this cylindrical section 16 and the surface to be coated (α₈). As a result, this border section is made liquid-tight. In this state, the coating liquid 28 is continuously supplied through the liquid supply pipe 29 into the space surrounded by the surface to be coated (α₈) and the inner surfaces of the masking cover 32 a and the container 39. As a result, the air within this space is drained through the drain hole 34 to the exterior, and the interior of this space is filled with the coating liquid 28. Consequently, this coating liquid 28 is brought into contact with the entire surface to be coated (α₈).

In the case of the present embodiment, since the smaller diameter side end section of the conical cylinder section 41 is inserted into the interior of the cylindrical section 16, an annular liquid pool section 43 whose cross section is triangular shaped is formed between the outer peripheral surface of the conical cylindrical section 41 and the inner peripheral surface of the cylindrical section 16, and the coating liquid 28 pools in this liquid pool section 43. However, the coating liquid 28 pooled in this liquid pool section 43 is drained to the radial direction inner side of the conical cylindrical section 41 through the inner sides of the respective cutouts 42 when the coating liquid 28 in the space is drained to the exterior through the drain hole 34. As a result, in the case of the present embodiment, thereafter, when the inner periphery of the outside end section of the cylindrical section 16 is separated from the outer peripheral surface of the conical cylindrical section 41, defacement of the surrounding sections by the coating liquid due to the coating liquid 28 pooled in the liquid pool section 43 can be prevented. On the other hand, if the respective cutouts 42 are not formed, as shown with an arrow in FIG. 6, there would be a problem of the coating liquid 28 pooled in the liquid pool section 43 dripping from the outside end periphery of the cylindrical section 16 to the outer peripheral surface of the conical cylindrical section 41 and so forth, and furthermore, of splash-back from these places and attachment onto parts on the surface of the hub main body 13 b other than the surface to be coated (α₈). Other constructions and effects are similar to those of the embodiment 1 shown in FIG. 1 and FIG. 2 described above.

EMBODIMENT 4

Next, FIG. 7 shows an embodiment 4 of the present invention. In the case of the present embodiment, the tip end section (top end section in FIG. 7) of the air nozzle 35 provided passing through the bottom section 40 of the container 39 so as to be liquid-tight is arranged on the radial direction inner side of the cylindrical section 16 that constitutes the hub main body 13 b. Meanwhile, the top end opening of the air nozzle 35 is made to oppose to the outside end surface of the hub main body 13 b. As a result, the air ejected from the top end opening of the air nozzle 35 is made to flow along the outside end surface of the hub main body 13 b and the inner peripheral surface of the cylindrical section 16 to blow from above on the coating liquid pooled in the liquid pool section 43. Accordingly the coating liquid pooled in this liquid pool section 43 is able to be easily drained to the radial direction inner side of this masking cover 32 a through the plurality of cutouts 42 provided in the top end edge of the masking cover 32 a. Other constructions and effects are similar to those of the embodiment 3 described above.

EMBODIMENT 5

Next, FIG. 8 shows an embodiment 5 of the present invention. In the case of the present embodiment, the outside end surface and inner peripheral surface of the cylindrical section 16 that constitutes the hub main body 13 b, and a part of the outside end surface of the hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16 (the part shown with the broken line α₇ in FIG. 8 and FIG. 27 (G)), is the surface to be coated. Accordingly, in the case of the present embodiment, when carrying out the operation of electrodepositing the coating particles on this surface to be coated (α₇), as shown in the diagram, the part close to the top end of the inner peripheral surface of the masking cover 32 b, which is constructed in a substantially cylindrical shape, is elastically pressed against the entire outer periphery part of the outside end surface of the cylindrical section 16. Accordingly, the border section between the surface to be coated (α₇) and the outer peripheral surface of the cylindrical section 16 is separated so as to be liquid tight. Other constructions and effects are similar to those of the embodiment 3 shown in FIG. 4 described above.

EMBODIMENT 6

Next, FIG. 9 shows an embodiment 6 of the present invention. In the case of the present embodiment, when carrying out the operation of electrodepositing the coating particles on the surface to be coated (α₇) of the hub main body 13 a, as shown in the diagram, the top end edge part of the masking cover 32 c, which is constructed in a substantially cylindrical shape, is made to oppose closely the entire outer periphery part of the outside end surface of the cylindrical section 16 that constitutes the hub main body 13 a with an interval of approximately 0.5 mm for example. The electrodepositing operation is carried out, while allowing a small amount of the coating liquid 28 that has filled the space surrounded by the masking cover 32 c and the hub main body 13 a to flow out into the exterior space through a minute gap 45 formed between the top end edge part of the masking cover 32 c and the outer periphery part of the outside end surface of the cylindrical section 16.

In the case of the present embodiment in which the electrodepositing operation is carried out in this way, since the space (interior space) surrounded by the masking cover 32 c and the hub main body 13 a and the exterior space are connected via the minute gap 45, even if the coating liquid 28 filled in the space is drained to the exterior through a drain hole (not shown in the diagram), this interior space does not become vacuum. As a result, thereafter, when separating the masking cover 32 and cylindrical section 16 from each other, a problem of the coating liquid 28 attached on the surface to be coated (α₇) splashing around can be prevented. Other constructions and effects of the other parts are similar to those of the embodiment 5 described above.

Moreover, in the embodiment 6 described above, when carrying out the electrodepositing operation, the top end edge part of the masking cover 32 c is closely opposed to the entire outer periphery part of the outside end surface of the cylindrical section 16, however, instead of this, even in the case where only one part in the circumferential direction is closely opposed and the remaining part in the circumferential direction is liquid-tightly pressed, a similar effect can be achieved. This also applies to the embodiments 1 to 4 described above.

EMBODIMENT 7

Next, FIG. 10 shows an embodiment 7 of the present invention. In the case of the present embodiment, an outer peripheral surface of an outside half section and outside end surface of the cylindrical section 16 that constitutes the hub main body 13 b (the part shown with the broken line α₂ in FIG. 10 and FIG. 27 (B)) is the surface to be coated. In the case of the present embodiment, when carrying out the operation of electrodepositing the coating particles on this surface to be coated (α₂), as is the case with the conventional method shown in FIG. 28 and described above, the outside half section of the cylindrical section is dipped in the coating liquid 28 contained in a coating liquid tank 27 a. However, in the case of the present embodiment, this dipping operation is carried out with the inner periphery part of the outside end surface of the cylindrical section 16 elastically pressed against the entire outer peripheral surface of a masking cover 32 d constructed in a closed-ended conical cylindrical shape. Thus, during this dipping operation, the surface to be coated (α₂) and the inner peripheral surface of the cylindrical section 16 are separated by the border section so as to be liquid-tight, so that the inner peripheral surface of this cylindrical section 16 does not come into contact with the coating liquid 28. The masking cover 32 d is supported and fixed on a top surface of a supporting base 44 fixed to the coating liquid tank 27 a.

Moreover, in the case of the present embodiment, due to the coating liquid 28 being supplied and drained into the coating liquid tank 27 a through the liquid supply pipe 29, the position of the liquid level of the coating liquid 28 contained in this coating liquid tank 27 a can be raised or lowered. In the case of the present embodiment, when pressing the inner periphery part of the outside end surface of the cylindrical section 16 against the outer peripheral surface of the masking cover 32 d in order to carry out the operation of electrodepositing the coating particles on the surface to be coated (α₂) as described above, the position of the level of the coating liquid is set lower than the bottom surface of the masking cover 32 d. Then after the masking cover has been pressed as described above, the liquid level is raised up to the level of the top end edge of the coating liquid tank 27 a as shown in the drawing (the coating liquid 28 is overflowed above this top end edge). Moreover, after completion of the above electrodepositing operation, the position of the liquid level is lowered to below the bottom surface of the masking cover 32 d, and then the inner periphery part of the outside end surface of the cylindrical section 16 is separated from the outer peripheral surface of the masking cover 32 d. Other constructions and effects are similar to those of the respective embodiments described above.

In the respective embodiments described above, a method is employed in which the operation of forming a coating film by electrodeposition coating is carried out for a single hub body prior to assembly of a wheel support hub unit. However, in the case of carrying out a method of electrodeposition coating on a hub according to the first aspect of the present invention, as is the case with the conventional method shown in FIG. 28 and described above, the operation of forming the coating film by means of electrodeposition coating may also be carried out for an assembled wheel support hub unit.

EMBODIMENT 8

FIG. 11 and FIG. 12 show an embodiment 8 of the present invention. In the present embodiment, the hub main body 13 a that constitutes the wheel support hub unit 5 a shown in FIG. 26 and described above is the object of the embodiment, and electrodeposition coating is carried out on the outside end portion to middle portion of the outer peripheral surface, and the outside end surface and inner peripheral surface of the cylindrical section 16 that constitutes this hub main body 13 a, and on the part of the outside end surface of the hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16 (the part shown with the broken line α₆ in FIG. 11 and FIG. 12 and in FIG. 27 (F)). Therefore, in the case of the present embodiment, first, degreasing cleaning is carried out on the part shown with the broken line α₆, and then preprocessing such as chromate treatment is carried out as necessary (this may be omitted). Next, the operation of electrodepositing the coating particles on the part shown with the broken line α₆ is carried out. In the case of the present embodiment, this operation is carried out in two separate processes (first process, second process).

An operation of the first step is carried out using a coating device 46 shown in FIG. 30 mentioned above (hereinafter, referred to as “first coating device 46”). Specifically, as shown in FIG. 11, the entire outside end surface of the cylindrical section 16 that constitutes the hub main body 13 a is brought into contact with the surface of the coating liquid 28 filled in a coating liquid tank 48 that constitutes this first coating device 46. Meanwhile, an outer surface of a guide section 53 provided on a top end section of a nozzle 52 is made to oppose across its entirety the part of the outside end surface of this hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16, and the inner peripheral surface of this cylindrical section 16. In this state, by ejecting coating liquid 47 upwards from the top end opening of this nozzle 52, this ejected coating liquid 47 is made to flow through a gap part between the abovementioned surfaces opposing to each other, in a state where this gap part is entirely filled with the coating liquid 47. Thus, this coating liquid 47 is brought into contact respectively with the entire part of the outside end surface of the hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16, and with the entire inner peripheral surface of this cylindrical section 16.

Moreover, having passed the gap part between the surfaces opposing to each other, the coating liquid 47 discharged upwards from the top end opening of the nozzle 52 as described above is poured into the coating liquid 47 filled in the coating liquid tank 48. Then the coating liquid 47 in the coating liquid tank 48 overflows by the amount that has been poured in this way to the exterior from the top end edge of the coating liquid tank 48. The coating liquid 47 overflowed like this is recovered by a recovery tank 49 that constitutes the first coating device 46, and it is re-used as the coating liquid 47 to be discharged from the top end opening of the nozzle 52. This method of using the coating liquid 47 is commonly used in all of the coating devices used in the present embodiment and in embodiments 9 to 11 described later. In the example shown in the diagram, since the outside end surface of the cylindrical section 16 is in contact with the surface of the coating liquid 47 filled in the coating liquid tank 48 as described above, the coating liquid 47 splashed into the place on this surface into which the coating liquid 47 is poured can be prevented from splashing into the space out of the cylindrical section 16.

As described above, once the outside end surface and inner peripheral surface of the cylindrical section 16 and the part of the outside end surface of the hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16 have been brought into contact with the coating liquid 47, subsequently, in this state, an electric voltage is applied between an electrode not shown in the diagram that is in contact with another part of this coating liquid 47 and the hub main body 13 a (for example, this electrode side is connected to a positive pole and the hub main body 13 a side is connected to a negative pole). As a result, by ionizing the coating particles in the coating liquid 47 and electrodepositing these ionized coating particles on the part in contact with the coating liquid 47, an undried coating film 54 is formed on this part. The operation up to here is the operation of the first process.

Having completed the operation of the first process in as described above, the process proceeds to the operation of the second process. The operation of this second process is carried out using a second coating device 46 a such as is shown in FIG. 12. A basic construction of this second coating device is substantially the same as that of the first coating device mentioned above. However, in the case of the second coating device 46 a, the shape of a top end section of a nozzle 52 a is a simple cylindrical shape, and a top end edge of this nozzle 52 a is arranged below the liquid level of the coating liquid 47 filled in the coating liquid tank 48.

When carrying out the second process using this second coating device 46 a, the coating liquid 47 is continuously supplied into the coating liquid tank 48 from the top end opening of the nozzle 52 a. As a result, while the coating liquid 47 filled in the coating liquid tank 48 is overflowed to the exterior from the top end edge of this coating liquid tank 48, the outside end portion to middle portion of the cylindrical section 16 that constitutes the hub main body 13 a is dipped in the coating liquid 47. The reason for dipping the cylindrical section 16 while the coating liquid 47 is overflowed is to maintain a constant position of the liquid level of this coating liquid 47 and to appropriately regulate a range to be coated on the outer peripheral surface of the cylindrical section 16. Moreover, in the case of the present embodiment, in order to reduce the likelihood of undulation occurring on the part on radial direction outer side of the cylindrical section 16, the top end opening of the nozzle 52 a is arranged on the radial direction inner side of the cylindrical section 16 and the coating liquid 47 is gently discharged from the top end opening of this nozzle 52 a.

Once the outside end surface and the outside end portion to middle portion of the outer peripheral surface and inner peripheral surface of this cylindrical section 16 have been brought into contact with the coating liquid 47 by dipping the outside end portion to middle portion of the cylindrical section 16 in the coating liquid 47 filled in the coating tank 48 as descried above, subsequently, in this state, an electric voltage is applied between an electrode not shown in the diagram that is in contact with another part of the coating liquid 47 and the hub main body 13 a (for examples this electrode side is connected to a positive pole and the hub main body 13 a side is connected to a negative pole). As a result, by ionizing the coating particles in the coating liquid 47 and electrodepositing these ionized coating particles on the part in contact with the coating liquid 47, an undried coating film 54 is formed on this part. The operation up to here is the operation of the second step.

Once the undried coating film 54 has been formed entirely on the part shown with the broken line α₆ as described above, thereafter, this coating film 54 is baked onto the abovementioned surface by heating this undried coating film 54 to dry it, and then this coating film 54 is cooled down to complete the coating operation.

As described above, in the case of the method of electrodeposition coating on a hub of the present embodiment, the operation of pouring the coating liquid 47 discharged from the top end opening of the nozzle 52 on the part of the outside end surface of the hub main body 13 a, the circumference of which is surrounded by the cylindrical section 16 and on the inner peripheral surface of the cylindrical section 16 (first process) and the operation of dipping the outside end portion to middle portion of the cylindrical section 16 in the coating liquid 47 filled in the coating liquid tank 48 (second process) are separately carried out. As a result, when carrying out the operation of this second process, a problem of the coating liquid 47 discharged from the top end opening of the nozzle 52 (52 a) being poured down on the coating liquid 47 filled in the coating liquid tank 48 causing undulations on this coating liquid 47 can be prevented. Therefore, when carrying out the operation of the second process, the state in which the outside end portion to middle portion of the outer peripheral surface of the cylindrical section 16 is in contact with the coating liquid 47 can be stabilized. As a result, in the case of the present embodiment, the coating film 54 can be accurately formed on the entire part shown with the broken line α₆ including the outside end portion to middle portion of the outer peripheral surface of the cylindrical section 16.

EMBODIMENT 9

FIG. 13 and FIG. 14 show an embodiment 9 of the present invention. In the present embodiment, the hub main body 13 that constitutes the wheel support hub unit 5 shown in FIG. 25 and described above is the object of the embodiment, and electrodeposition coating is done on the outside end portion to middle portion of the outer peripheral surface, the outside end surface and inner peripheral surface of the cylindrical section 16 that constitutes this hub main body 13, and on the radial direction outer half portion of the part of the outside end surface of the hub main body 13, the circumference of which is surrounded by the cylindrical section 16 (the part shown with the broken line α₄ in FIG. 13 and FIG. 14 and in FIG. 27 (F)). The reason for not carrying out electrodepositing on the radial direction inner half portion of the part on the outside end surface of the hub main body 13, the circumference of which is surrounded by the cylindrical section is that this radial direction inner half portion is a bearing surface of a nut 25 (refer to FIG. 25) and if this radial direction inner half section is subjected to electrodeposition coating, the nut 25 is likely to become loose.

Consequently, in the case of the present embodiment, in order not to have the coating liquid 47 discharged from the top end section of the nozzle 52 b that constitutes a first coating device 46 b come into contact with the radial direction inner half section when carrying out the operation of the first process as shown in FIG. 13 (and furthermore in order not to have the coating liquid 47 come into contact with the inner peripheral surface of a spline hole 22), the radial direction inner half section and an outside end opening of the spline hole 22 are covered by a masking cover 55. This masking cover 55 is manufactured from elastic materials such as rubber and synthetic resin, in a truncated cone shape, and a bottom plate section 56, which is an end section on a smaller diameter side (down side in FIG. 13), is supported and fixed on the top end section of the nozzle 52 b, and its opening periphery on a greater diameter side (upper side in FIG. 13) is pressed entirely against the outside end surface of the hub main body 13 so as to be liquid-tight. Moreover, a mesh section 57 through which the coating liquid 47 can pass freely is provided in a part between the masking cover 55 and the guide section 53 around the entire circumference on the top end section of the nozzle 52 b. The coating liquid 47 can be discharged from the top end section of the nozzle 52 b through this mesh section 57. In the case of the present embodiment, as is the case with the embodiment 8 described above, the operation of the following second step is carried out using the second coating device 46 a as shown in FIG. 14. Other constructions and effects are similar to those of the embodiment 8 described above.

EMBODIMENT 10

Next, FIG. 15 and FIG. 16 show an embodiment 10 of the present invention. In the embodiment 8 shown in FIG. 11 and FIG. 12 mentioned above, a method of carrying out the operation of the first process and the operation of the second process respectively using different coating devices 46 and 46 a was employed. In contrast to this, in the case of the present embodiment, a method of carrying out each operation of the first and second processes using one coating device 46 c such as is shown in FIG. 15 and FIG. 16 is employed. The basic construction of the coating device 46 c used in the present embodiment is substantially the same as that of the first coating device 46 used in the embodiment 8 mentioned above. However, in the case of the coating device 46 c of the present embodiment, the nozzle 52 can be shifted in an axial direction (vertical direction in FIG. 15 and FIG. 16) with respect to the coating liquid tank 48 and the recovery tank 49. Therefore, in the case of the present embodiment, annular sealing devices 60 are respectively installed on the inner peripheries of through holes 58 and 59 formed in the respective bottom plate sections 50 and 51 that constitute the coating liquid tank 48 and the recovery tank 49, and the inner peripheries of the respective sealing devices 60 are respectively brought into contact with an outer peripheral surface of a middle section of the nozzle 52 to secure sufficient sealing while allowing sliding in the axial direction.

In the case of the present embodiment, when carrying out the operation of the first process using the coating device 26 c, as shown in FIG. 15, the top end opening of the nozzle 52 is arranged above the surface of the coating liquid 47 filled in the coating liquid tank 48. In this state, as shown in the same diagram, the operation of the first process is carried out in a similar manner to the embodiment 8 described above. Subsequently, when carrying out the operation of the second process, as shown in FIG. 15 and FIG. 16, by shifting the top end opening of the nozzle 52 downward, the top end opening of this nozzle 52 is arranged below the liquid surface of the coating liquid 47 filled in the coating liquid tank 48. Meanwhile, by shifting either one of the coating device 46 c or the hub main body 13 a, or both of them in a direction such that they move relatively closer to each other in the axial direction (vertical direction in FIG. 15 and FIG. 16), the outside end portion to middle portion of the cylindrical section 16 that constitutes the hub main body 13 a is dipped in the coating liquid 47. In this state, as shown in FIG. 16, the operation of the second process is carried out in a similar manner to the embodiment 8 described above.

In the case of the present embodiment described above, since the operations of the first and second processes are carried out using the single coating device 46 c, a reduction in operation time, operation space and cost of the operation device can be achieved compared to the case of the embodiment 8 described above. Other constructions and effects are similar to those of the embodiment 8 described above.

EMBODIMENT 11

Next, FIG. 17 and FIG. 18 show an embodiment 11 of the present invention. In the embodiment 9 shown in FIG. 13 and FIG. 14 mentioned above, a method of carrying out the operation of the first process and the operation of the second process respectively using the different coating devices 46 b and 46 a was employed. In contrast to this, in the case of the present embodiment, a method of carrying out each operation of the first and second steps using one coating device 46 d such as is shown in FIG. 17 and FIG. 18 is employed. The basic construction of the coating device 46 d used in the present embodiment is substantially the same as that of the first coating device 46 b used in the embodiment 9 mentioned above. However, in the case of the coating device 46 d of the present embodiment, the nozzle 52 b can be shifted in an axial direction (vertical direction in FIG. 17 and FIG. 18) with respect to the coating liquid tank 48 and the recovery tank 49. Therefore, in the case of the present embodiment, annular sealing devices 60 are respectively installed on the inner peripheries of through holes 58 and 59 formed in the respective bottom plate sections 50 and 51 that constitute the coating liquid tank 48 and the recovery tank 49, and the inner peripheries of the respective sealing devices 60 are respectively brought into contact with an outer peripheral surface of a middle section of the nozzle 52 b to secure sufficient sealing while allowing sliding in the axial direction.

In the case of the present embodiment, when carrying out the operation of the first process using the coating device 46 d, as shown in FIG. 17, the mesh section 57 being the top end opening of the nozzle 52 b is arranged above the liquid surface of the coating liquid 47 filled in the coating liquid tank 48. In this state, as shown in the same diagram, the operation of the first step is carried out in a similar manner to the embodiment 9 described above. Subsequently, when carrying out the operation of the second process, as shown in FIG. 17 and FIG. 18, by shifting the nozzle 52 b downward, the guide section 53 and the mesh section 57 provided on the top end portion of this nozzle 52 b are arranged below the liquid level of the coating liquid 47 filled in the coating liquid tank 48. However, at this time, at least the top end section of the masking cover 55 is arranged above the liquid level of the coating liquid 47 so as not to allow the coating liquid 47 to enter the interior (in a concaved section provided on the top surface) of this masking cover 55. Meanwhile, by shifting either one of the coating device 46 d or the hub main body 13, or both of them in a direction such that they move relatively closer to each other in the axial direction (vertical direction in FIG. 17 and FIG. 18), the outside end portion to middle portion of the cylindrical section 16 that constitutes the hub main body 13 is dipped in the coating liquid 47. In this state, as shown in FIG. 18, the operation of the second process is carried out in a similar manner to the embodiment 9 described above.

In the case of the present embodiment described above, since the operations of the first and second processes are carried out using the single coating device 46 d, a reduction in operation time, operation space and cost of the operation device can be achieved compared to the case of the embodiment 9 described above. Other constructions and effects are similar to those of the embodiment 9 described above.

In the embodiments 8 to 11 described above, as the nozzles 52 and 52 b that constitute the coating devices 46, 46 b, and 46 c, the nozzles 52 and 52 b having the guide section 53 provided on the top end sections thereof are used, however, this guide section 53 may be omitted. This also applies to the nozzle 52 that constitutes the coating device 46 shown in FIG. 30 described above.

Moreover, in the embodiments 8 to 11 mentioned above, the method of electrodeposition coating on a hub according to the second aspect of the present invention is carried out for a hub (hub main body 13 a) that constitutes a wheel support hub unit 5 a for a driven wheel shown in FIG. 26 mentioned above, and for a hub (hub main body 13) that constitutes a wheel support hub unit 5 for a driving wheel shown in FIG. 25 mentioned above. However, the method of electrodeposition coating on a hub according to the second aspect of the present invention is not limited to these and may also be carried out for a hub that constitutes a wheel support hub unit having various kinds of structure (including one in which an outside inner ring raceway is directly formed on the middle section of the outer peripheral surface of the hub, and one in which this outside inner ring raceway is formed on the outer peripheral surface of a separate inner ring that is fitted onto the middle section of the hub).

Furthermore, in the embodiments 8 to 11 described above, a method is employed in which the operation of forming a coating film by electrodeposition coating is carried out for a single hub body prior to assembly of a wheel support hub unit. However, in the case of carrying out the method of electrodeposition coating on a hub according to the second aspect of the present invention, the operation of forming the coating film by means of electrodeposition coating may also be carried out for an assembled wheel support hub unit.

When manufacturing the respective wheel support hub units 5 and 5 a shown in FIG. 25 and FIG. 26 mentioned above, by carrying out a forging process such as rolling press processing to a cylindrical section present at an inside end section of the hub main bodies 13 and 13 a, this cylindrical section is plastically deformed outward in the radial direction to form a crimped section 19 in this part. In the case where the operation of forming such a crimped section 19 is carried out after carrying out any of the embodiments 8 to 11 described above for example, if the part on which the coating film 54 has been formed (for example, the part of the outside end surface of the respective hub main bodies 13 and 13 a, the circumference of which is surrounded by the cylindrical section 16 and the inner peripheral surface of this cylindrical section 16) is employed as an abutment (a surface that comes in contact with a seat), the force applied during processing may peel off the coating film 54. Therefore, in order to prevent this kind of problem from occurring, it is preferable that a part on which the coating film 54 is not formed (for example, an outside surface of an attachment flange 15) be employed as the abutment.

EMBODIMENT 12

FIG. 19 to FIG. 22 show an embodiment 12 of the present invention. In the present embodiment the hub main body 13 a shown in FIG. 19 is an object of the embodiment. The hub main body 13 a is a constructing member of the wheel support hub unit 5 a shown in FIG. 26 mentioned above. In the example shown in the diagram, a high frequency hardening processing is applied to the entirety of the middle section of the outer peripheral surface of the hub main body 13 a including an inner ring raceway 17 a (the part shown in cross hatching pattern) to form a hardened layer 61 on this part. By forming such a hardened layer 61, the durability of the hub main body 13 a is increased.

In the case of the present embodiment, electrodeposition coating is carried out on the outer peripheral surface, inner peripheral surface and outside end surface of the cylindrical section 16 provided on the outside end section of the hub main body 13 a, and the radial direction middle section of the outside end surface of this hub main body 13 a (the part shown with the broken line α in FIG. 19). Therefore in the case of the present embodiment, first, a predetermined preprocessing such as degreasing cleaning is carried out on the part shown with the broken line α, and then with this part shown with the broken line α in contact with (dipped in) the coating liquid (not shown in the diagram), an electric voltage is applied between an electrode (not shown in the diagram) in contact with another part of this coating liquid and another electrode (not shown in the diagram) in contact with the hub main body 13 a (the coating liquid side is connected to a positive pole and the hub main body 13 a side is connected to a negative pole). As a result, by ionizing the coating particles in the coating liquid and electrodepositing these ionized coating particles on the part shown with the broken line α, an undried coating film 62 is formed on this part. In the example shown in the diagram, this coating film 62 is shown with a heavy line for the sake of simplicity, however, the width of this heavy line does not represent the thickness of this coating film 62. The actual thickness of the coating film 62 is, for example, approximately several μm after being subjected to baking, depending on the length of time for which the above mentioned electric voltage has been applied.

Then, having formed the undried coating film 62 as described above, this undried coating film 62 is heated using far-infrared radiation emitted from a ceramic heater 63 as shown in FIG. 21. As a result, the undried coating film 62 is dried and this coating film 62 is baked onto the surface of the hub main body 13 a. In the case of the present embodiment, the temperature to which the coating film 62 is heated at this time is no greater than 140° C.

Once the coating film 62 has been baked onto the surface of the hub main body 13 a as described above, subsequently, this coating film 62 is cooled down by blowing cold air ejected from a cooler 64 onto the coating film 62, as shown in FIG. 22, to complete the coating operation.

As described above, in the case of the method of electrodeposition coating on a hub according to the present embodiment, the heating temperature of the undried coating film 62 is low, no greater than 140° C. As a result, even in the case where the heat applied to this coating film 62 is transmitted to the hardened layer 61 formed on the middle section of the outer peripheral surface of the hub main body 13 a, the temperature of this hardened layer 31 does not excessively rise (does not rise to a temperature where a softening effect such as annealing or tempering starts to occur in this hardened layer 61). Therefore, in the case of the present embodiment, when forming the coating film 62, a decrease in the hardness of the hardened layer 61 can be prevented.

EMBODIMENT 13

Next, FIG. 23 and FIG. 24 show an embodiment 13 of the present invention. In the case of the present embodiment, a procedure of the operation for forming the undried coating film 62 on the part shown with the broken line α in FIG. 19 mentioned above, as shown in FIG. 20 mentioned above, by electrodepositing ionized coating particles on the part in question, is similar to that in the case of the embodiment 12 described above.

In the case of the present embodiment, having formed the undried coating film 62 as described above, cold air ejected from a cooler 64 a is blown onto the middle section (the part on which the hardened layer 61 has been formed) to the inside end section of the hub main body 13 a as shown in FIG. 23. Thus, while cooling down this part, the undried coating film 62 is heated by the far-infrared radiation emitted from the ceramic heater 63. As a result, the coating film 62 is dried and this coating film 62 is baked onto the surface of the hub main body 13 a. In the case of the present embodiment, the heating temperature of the coating film 62 at this time is regulated within a range of 140° C. to 220° C.

Then, once the coating film 62 has been baked onto the surface of the hub main body 13 a as described above, subsequently, the coating film 62 is cooled down by blowing cold air discharged from the cooler 64 a on the middle section to the inside end section (the section on which the hardened layer 61 is formed) of the hub main body 13 a, while cold air discharged from the cooler 64 is directly blown onto the coating film 62, to complete the coating operation.

As described above, in the case of the method of electrodeposition coating on a hub according to the present embodiment, the heating temperature for the undried coating film 62 is raised comparatively high within a range from 140° C. to 220° C., however, the operation of heating the undried coating film 62 is carried out while cooling the middle section to the inside end section of the hub main body 13 a. As a result, an increase in the temperature of the hardened layer 61 due to the heat applied to the coating film 62 can be suppressed. Therefore, an excessive increase in the temperature of the hardened layer 61 can be prevented (such that it does not rise to the temperature where a softening effect such as annealing or tempering starts to occur in this hardened layer 61). As a result, in the case of the present embodiment also, when forming the coating film 62, a decrease in the hardness of the hardened layer 61 can be prevented. Furthermore, in the case of the present embodiment, since the heating temperature of the undried coating film 62 is raised comparatively high, a length of time required for baking this coating film 62 can be shortened compared to the case of the embodiment 12 described above.

Moreover, in the embodiments 12 and 13, a method of electrodeposition coating on a hub according to a third and fourth aspects of the present invention is carried out for a hub (hub main body 13 a) that constitutes the wheel support hub unit for a driven wheel shown in FIG. 26 mentioned above. However, the method of electrodeposition coating on a hub according to the third and fourth aspects of the present invention may also be carried out for a hub (hub main body 13) that constitutes the wheel support hub unit 5 for a driving wheel shown in FIG. 25 mentioned above. Furthermore, the method of electrodeposition coating on a hub is not limited to this and may also be carried out for a hub that constitutes a wheel support hub unit that has various kinds of structure (including one in which an outside inner ring raceway is directly formed on the middle section of the outer peripheral surface of the hub, and one in which this outside inner ring raceway is formed on the outer peripheral surface of a separate inner ring that externally engages with the middle section of the hub).

Furthermore, in the embodiments 12 to 13 described above, a method is employed in which the operation of forming a coating film by electrodeposition coating is carried out for a single hub body prior to assembly of a wheel support hub unit. However, in the case of carrying out the method of electrodeposition coating on a hub according to the third and fourth aspects of the present invention, the operation of forming the coating film by means of electrodeposition coating may also be carried out for an assembled wheel support hub unit. In the case of carrying out the method of electrodeposition coating on a hub for an assembled wheel support hub unit as mentioned above, in addition to the effects described in the aforementioned embodiments 12 and 13, an effect of preventing heat deterioration of grease enclosed in a rolling body installation section when forming the coating film can also be achieved.

INDUSTRIAL APPLICABILITY

An antirust coating film can be accurately formed only within a desired range on a cylindrical section provided on an outside end section of a hub that constitutes a wheel support hub unit by means of electrodeposition coating, without using masking tape, and without influencing a part of an outer peripheral surface of the hub on which a hardened layer has been formed by means of high frequency hardening processing, nor grease enclosed in a rolling body installation section. 

1. A method of electrodeposition coating on a hub where in order to form a coating film on a desired range that includes at least one part of a surface of a cylindrical section among the surfaces of a hub that constitutes a wheel support hub unit that is respectively provided with an attachment flange on a part close to an outside end of an outer peripheral surface for supporting and fixing a wheel and a braking rotating member, and with the cylindrical section for externally engaging at least one of the wheel and the braking rotating member on an outside end section, coating particles in a coating liquid are electrodeposited on this desired range, with the desired range in contact with the coating liquids wherein the operation of electrodepositing the coating particles on the desired range is carried out with a masking cover in contact with or closely opposing to a border part on the surface of the hub between the desired range and a range adjacent to this desired range.
 2. A method of electrodeposition coating on a hub according to claim 1, wherein a border sections which is to come into contact with, or closely oppose, the masking cover, is a periphery part of an outside end surface of a cylindrical section that constitutes the hub.
 3. A method of electrodeposition coating on a hub according to claim 1, wherein a hole that passes through the hub in an axial direction is provided in a center section of the hub, and a border section, which is to come into contact with, or closely oppose, the masking cover, is an annular section that surrounds an outside end opening of the hole of the outside end surface of the hub which is surrounded by the cylindrical section.
 4. A method of electrodeposition coating on a hub according to claim 2, wherein after coating particles in a coating liquid have been electrodeposited onto an inner surface of a cylindrical section that constitutes the hub in a state where a radial direction inner side of the cylindrical section is filled with the coating liquid, this coating liquid is drained to the exterior of this cylindrical section through an outside end opening of the cylindrical section, after which gas is blown into the outside end opening of this cylindrical section.
 5. A method of electrodeposition coating on a hub according to claim 1, wherein, as the masking cover, a masking cover is used, which has an entirely cylindrical shape, a section on the outer peripheral surface thereof close to a tip end that can be pressed against the entire inner periphery part of the outside end surface of the cylindrical section that constitutes the hub so as to be liquid-tight, and a liquid drained passage formed on a part of the tip end section able to enter within the cylindrical section that connects the outer peripheral surface and inner peripheral surface of said portion.
 6. A method of electrodeposition coating on a hub where in order to form a coating film on a desired range that includes at least a surface of a cylindrical section among the surfaces of a hub that constitutes a wheel support hub unit that is respectively provided with an attachment flange on a part close to an outside end of an outer peripheral surface for supporting and fixing a wheel and a braking rotating member, and with the cylindrical section for externally engaging at least one of these wheel and braking rotating member on an outside end section, coating particles in a coating liquid are electrodeposited on this desired range, with the desired range in contact with the coating liquid, wherein a plurality of partial ranges that respectively become a range of one part of the desired range are set, and the operation of electrodepositing said coating particles on the desired range is carried out in separate processes for each of said partial ranges.
 7. A method of electrodeposition coating on a hub according to claim 6, wherein one of the respective processes is a process of electrodepositing the coating particles onto a section among the surfaces of the cylindrical section that is in contact with the coating liquid while only the cylindrical section is dipped in the coating liquid contained in a coating liquid tank having an open top section.
 8. A method of electrodeposition coating on a hub according to claim 6, wherein a plurality of coating devices at least provided with coating liquid tanks that contain the coating liquid, and having an open top end, are prepared, and one coating device is selected among the respective coating devices for each process, and the selected coating device is used to carry out the process.
 9. A method of electrodeposition coating on a hub according to claim 6, wherein one coating device provided with a coating liquid tank that contains coating liquid and that has an open top end, and a nozzle that sprays the coating liquid upwards is prepared, and each step is performed using only this coating device.
 10. A method of electrodeposition coating on a hub according to claim 9, wherein relative positions of liquid levels of the coating liquid contained in the coating liquid tank and of the nozzle to the hub, and a way of spraying the coating liquid to be sprayed from this nozzle are changed for each of the steps.
 11. A method of electrodeposition coating on a hub where, after forming an undried coating film on a surface of a cylindrical section among the surfaces of a hub that constitutes a wheel support hub unit respectively provided with an attachment flange on a part close to an outside end of an outer peripheral surface for supporting and fixing a wheel and a braking rotating member, and with the cylindrical section for externally engaging at least one of the wheel and the braking rotating member on an outside end section, by electrodepositing coating particles onto the surface, the coating film is baked onto the surface of the cylindrical section by heating the undried coating film to dry it, wherein the heating temperature of the undried coating film is below 140° C.
 12. A method of electrodeposition coating on a hub where, after forming an undried coating film on a surface of a cylindrical section among the surfaces of a hub that constitutes a wheel support hub unit respectively provided with an attachment flange on a part close to an outside end of an outer peripheral surface for supporting and fixing a wheel and a braking rotating member, and with the cylindrical section for externally engaging at least one of the wheel and the braking rotating member on an outside end section, by electrodepositing coating particles onto the surface, the coating film is baked onto the surface of the cylindrical section by heating the undried coating film to dry it, wherein the heating temperature of the undried coating film is between 140° C. and 220° C., and the operation of heating the undried coating film is carried out while the hub is being cooled from an inside end side. 